Method for separating a gas mixture

ABSTRACT

New carbon nanomaterials, preferably titanium carbide-derived carbon (CDC) nanoparticles, were embedded into a polyamide film to give CDC/polyamide mixed matrix membranes by the interfacial polymerization reaction of an aliphatic diamine, e.g., piperazine, and an activated aromatic dicarboxylate, e.g., isophthaloyl chloride, supported on a sulfone-containing polymer, e.g., polysulfone (PSF), layer, which is preferably previously prepared by dry/wet phase inversion. The inventive membranes can separate CO 2  (or other gases) from mixtures of CO 2  and further gases, esp. CH 4 , based upon the generally selective nanocomposite layer(s) of CDC/polyamide.

BACKGROUND OF THE INVENTION Field of the Invention

This application relates to gas separation, particularly CO₂ separation,membranes useful for gas separation, and methods of making suchmembranes.

DESCRIPTION OF THE RELATED ART

Gas separation using membranes, particularly polymer membranes, has beena subject of research interest for several decades. Gas separation is ofparticular interest to petroleum producers and refiners, chemicalcompanies, and industrial gas suppliers. Certain separations have beenimplemented commercially, such as carbon dioxide (CO₂) removal fromnatural gas, fermentation gases, and in enhanced oil recovery, as hashydrogen (H₂) removal from nitrogen (N₂), methane (CH₄), argon, andammonia (NH₃).

Membranes used in commercial gas separation applications are oftenpolymeric and nonporous, with separations being based on asolution-diffusion mechanism involving molecular-scale interactions ofthe permeating gas with the membrane polymer. Solution-diffusion assumesa membrane having two opposing surfaces, with components being adsorbedby the membrane at one surface, transported through the membrane by agas concentration gradient, and desorbed at the opposing surface.Membrane separation performance for a given pair of gases, e.g.,CO₂/CH₄, O₂/N₂, H₂/CH₄, can be evaluated by (1) the permeabilitycoefficient of the membrane and (2) the selectivity of the membrane. Thepermeability coefficient is the product of the gas flux and the membraneskin thickness, divided by the pressure difference across the membrane.Selectivity is the ratio of the permeability coefficients of the twogases, the more permeable gas over the less permeable. Relevant factors,such as the diffusion coefficient and the solubility coefficient,respectively decrease and increase (generally) with increasing molecularsize of the gas. Higher permeability allows a reduction in the membranearea necessary to treat a given volume of gas, and higher selectivityprovides higher purity product gas.

Polymeric membrane materials are often used by contacting a feed gasmixture on an upstream side of the membrane, giving a permeate mixtureon the membrane's downstream side with a greater concentration of one ofthe components from the feed mixture relative to the original feed gasmixture composition. Maintaining a pressure differential between theupstream and downstream sides can be used to drive permeation. Thedownstream side can be maintained at an underpressure, and/or theupstream side can be maintained at an overpressure, i.e., upstreamshould be higher pressure than downstream.

Various materials, such as fibers, porous supports, etc., have beenincorporated into polymeric membranes, e.g., to provide mechanicalstrength to the membranes. Some composite materials have shown improvedliquid separation properties over the polymer material themselves.Membrane materials with incorporated materials within a polymericmatrix, e.g., Type 5A zeolites into silicone rubber, a hydrophobiccrystalline silica-based zeolite into silicone rubber or celluloseacetate, Type 4A zeolite into polyethersulfone, zeolite 4A intopolyetherimide, etc., have also been used for gas separations. However,at least some of these have suffered equilibration to steady state afteradsorption site saturation.

Accordingly, further research has been conducted into different materialfor use in polymer membrane gas separation. For example, US 2014/0210118A1 by Lee et al. (Lee) discloses a polymer or polymer composite membranehaving through-thickness micropores and its preparation Thepolymer/composite membrane has a pore structure in which micropores arealigned in a mesh structure in the thickness direction of the polymer orpolymer composite membrane due to unidirectional freezing in thethickness direction of a solvent. Lee's membrane has through-thicknessmicropores, and has permeability in the thickness direction and superioruniformity in size of the micropores and wall thickness between themicropores. Lee reports that the membrane can be used as a porousmembrane substrate, microfiltration membrane, etc., but specificallydescribes its use as a battery separator.

Lee only discloses using fluorine-based (co)polymers, based onvinylidene fluoride (VDF), tetrafluoroethylene (TFE),ethylenetetrafluoroethylene (ETFE), perfluoroalkoxyalkane (PFA),vinylfluoride (VF), chlorotrifluoroethylene (CTFE), fluorinated ethylenepropylene (FEP), hexafluoropropylene (HFP), and/or perfluoro (propylvinylether), and hydrophobic polymers, including polyethylene,polypropylene, polysulfone, polyketone, polyethersulfone, cellulose,cellulose acetate, cellulose triacetate, regenerative cellulose, acrylresin, nylon, polyamide, epoxy, and polyimide-based (co)polymers. Lee'spolymer may include inorganic materials, such as titanium oxide, (fumed)silica, silicon carbide, silicon nitride, spinel, silicon oxycarbide,glass powder, glass fiber, carbon fiber, graphene, nanotubes, goldmicroparticles, silver microparticles, alumina, magnesia, siliconnitride, zirconia, zirconium carbide, sialon, nasicon, silceram,mullite, aluminum, copper, nickel, steel, titanium, titanium carbide,and titanium diborate. However, Lee does not disclose a multi-layermembrane, nor does Lee disclose a polyamide membrane or theincorporation of CDC into the polyamide layer to fabricate the mixedmatrix membrane. Furthermore, Lee does not disclose separating carbondioxide from methane.

US 2012/0093709 A1 by Gogotsi et al. (Gogotsi) discloses a method forproducing a nanoporous carbide-derived carbon (CDC) composition with atunable pore structure and a narrow pore size, as well as compositionsprepared by the method. Gogotsi describes exposing a metal carbide to ahalogen, e.g., fluorine, chlorine, bromine, and/or iodine, so that themetal is extracted from the carbide. Gogotsi describes relevant metalcarbides to include SiC, TiC, ZrC, B₄C, TaC, Mo₂C, and Ti₃SiC₂. Gogotsidescribes using its compositions in, e.g., molecular sieves, gasstorage, catalysts, adsorbents, battery electrodes, supercapacitors,water or air filters, and medical devices.

However, Gogotsi discloses neither a polyamide membrane nor amulti-layer membrane. Moreover, Gogotsi provides no information on usingCDC as fillers to prepare the mixed matrix membrane. Gogotsi does notdisclose separating CO₂ from methane.

Nature Materials 2013, 2(9), 591-594 by Gogotsi et al. (Gogotsi NPL)discloses carbide-derived carbons (CDCs) as nanoporous carbons withporosity that can be tuned with sub-Angstrom accuracy in the range 0.5to 2 nm. The Gogotsi NPL states that CDCs have a narrower pore sizedistribution than single-wall carbon nanotubes or activated carbons, andthat CDC pore size distribution is comparable with that of zeolites. TheGogotsi NPL describes producing CDCs at temperatures from 200 to 1200°C. as powders, coatings, membranes, or parts with near-final shapes,with or without mesopores. The Gogotsi NPL states that molecular sieves,gas storage, catalysts, adsorbents, battery electrodes, supercapacitors,water/air filters, and medical devices could be applications for itsCDCs.

The Gogotsi NPL discloses making CDCs from Ti₃SiC₂, TiC, SiC, anddescribes that CDCs can be made from SiC, TiC, ZrC, B₄C, TaC, Mo₂C andmany others. The Gogotsi NPL does not disclose preparing a polyamidemembrane, nor a multi-layer membrane, nor using CDC as fillers in amixed matrix membrane. Additionally, the Gogotsi NPL does not discloseseparating gases, much less separating CO₂ from methane.

WO 2012/119994 A2 by Aabloo et al. (Aabloo), which cites Gogotsi andother CDC references, discloses a sensor material used, e.g., inrobotics, biotechnology, and (bio)medicine, wherein the sensor materialis manufactured from carbon-ionic liquid-polymer composite, comprisingat least two separator layers, which are made from carbon-ionicliquid-polymer composite material and comprise at least two electrodelayers manufactured of carbon film and separated by a layer manufacturedas porous polymer membrane comprising an ionic liquid not havingelectronic conductivity. At the same time Aabloo's sensor material actsas actuator, which allows immediate feedback of the actuator curvature,its velocity and change of direction of movement.

Aabloo describes carbide-derived carbon material (CDC) from TiC, B₄C,and Mo₂C, treated at varied temperatures to vary pore distribution incarbon material, and aggregated in an electrode layer withpoly(vinylidene difluoridehexafluoropropylene) (PVdF(HFP)). Aabloodescribes that fluoropolymers can generally be used, as well ascellulose-based polymers. However, Aabloo discloses no polyamidemembrane, nor a multi-layer membrane. Aabloo does not discloseseparating gases with its membrane, let alone CO₂ from methane.

Desalination 2017, 420, 125-135, by Khan et al. (Khan) disclosesimproving the fouling resistance of reverse osmosis (RO) membranes, acharacteristic that is a valuable property in the desalination industry.Khan reports the preparation of carbide derived carbon (CDC)/polyamidehybrid membrane, aiming to improve the fouling-resistance of ROmembranes. TEM images of Khan's CDC particles show a mixture ofamorphous and ordered graphitized carbon and their degree of orderingthat is directly proportional to the chlorination temperature. SEMimages of Khan's membranes show a ridge-valley structure of aromaticpolyamide. Khan reports improved surface hydrophilicity of its membranecompared a control polyamide membrane. Desalination experiments showedthat the permeate flux increased 51%, 45%, and 38% under pure water,brackish water, and fouling conditions; respectively. Khan's controlmembrane lost 26% of its initial flux while a CDC-doped membrane lostonly 11.5% after 2 hours of continuous operation. Khan reports that CDCcan significantly enhance the fouling resistance and permeability of itspolyamide RO-membranes.

The master's thesis by Anwar ul Haq Khan entitled “Water DesalinationUsing Carbide Derived Carbon (CDC)/Mixed Matrix Membrane,” published inMay of 2016 in the Faculty of Chemical Engineering at the King FandUniversity of Petroleum & Minerals (Khan Thesis—incorporated herein byreference in its entirety) discloses microporous carbide derived carbons(CDCs) nanocarbon materials used as nanofiller in TFN membranes forwater desalination experiments. The Khan Thesis describes materialssimilar to those described in Khan, and discloses that membrane cleaningwith dilute NaOH solution was able to recover 97% of the original waterflux for reverse osmosis. The Khan Thesis recommends preparing aninorganic CDC membrane, testing long term membrane stability, checkingnano particle leaching, and covalently bonding the CDCs to the PA layer.

Khan discloses including CDC particles, prepared from TiC with Cl₂ at700, 800, and 900° C., in thin film nanocomposites (TFNs) and thin filmcomposites (TFCs) at concentrations 0.001, 0.002, 0.003, and 0.0033 w/v%), and polymers comprising units of m-phenylenediamine (MPD, an aryldiamine) and trimesoyl chloride (TMC, an aryl tri-carboxylic acidchloride), as well as a polysulfone (average MW ˜35,000) substrate for avery thin polyamide (PA) thin layer prepared by interfacialpolymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC).Khan does not disclose a polyamide including an aliphatic monomer, muchless an heteroatom substituted aliphatic amine having cyclical nitrogenatoms, e.g., piperazine, nor a di-carboxylic acid halide, such asisophthaloyl chloride (IPC) as monomers for a polyamide. Khan fails todisclose combining certain ratios of polysulfone, dimethyl acetamide(DMAc), and tetrahydofuran (THF), to prepare a polysulfone support.Moreover, Khan does not disclose separating gases, much less CO₂ frommethane.

Chemie Ing. Techn. 2013, 85(11), 1742-1748 by Martin et al. (Martin)discloses TiO₂/C and TiC/C composite nanofibers produced byelectrospinning of resin/TiCl₄ precursor solution. Martin's ceramicfiber webs were porous and showed surface areas as high as 523 m²/g.They were further converted to carbide-derived carbon (CDC) fibers underfull retention of the fiber-like shape and flexibility. Martin reports ahierarchical pore structure and a specific surface as high as 1378 m²/gfor CDC membranes, proposing high temperature filtration, catalystsupport, and energy storage as applications.

However, Martin does not disclose preparing multi-layer membranes.Martin discloses neither a polyamide membrane, nor the incorporation ofCDC into a polyamide layer, nor fabricating a mixed matrix membrane, norseparating CO₂ from methane.

U.S. Pat. No. 7,485,173 B1 and U.S. Pat. No. 7,806,962 (published as US2009/0031897 A1) to Liu et al. (Liu), disclose cross-linkable andcross-linked mixed matrix membranes and the use of such membranes forseparations such as for CO₂/CH₄, H₂/CH₄ and propylene/propaneseparations. Liu prepares cross-linkable and cross-linked mixed matrixmembranes (MMMs) by incorporating microporous molecular sieves orsoluble high surface area microporous polymers (PIMs) as dispersedmicroporous fillers into a continuous cross-linkable polymer matrix.Liu's cross-linked MMMs were prepared by UV-cross-linking thecross-linkable MMMs containing cross-linkable polymer matrix such asBP-55 polyimide. Liu reports that pure gas permeation test resultsdemonstrated that both types of MMMs exhibited higher performance forCO₂/CH₄ and H₂/CH₄ separations than those of the correspondingcross-linkable and cross-linked pure polymer matrices.

Liu uses a cross-linkable polymer, which may be any polymer containingUV-crosslinkable benzophenone, acrylic, vinyl, styrenic,styrenicacrylic, sulfonic, and/or 2,3-dihydrofuran group(s), such aspolyacrylates, polyimides such as poly[1,2,4,5-benzentetracarboxylicdianhydride-co-3,3′, 4,4′-benzophenonetetracarboxylicdianhydride-co-4,4′-methylenebis(2,6-dimethylaniline)] imides (e.g.,BP-55 with 1:1 ratio of 1,2,4,5-benzentetracarboxylic dianhydride and3,3′, 4,4′-benzophenonetetracarboxylic dianhydride in this polyimide);poly(styrenes), including styrene-containing copolymers such asacrylonitrilestyrene copolymers, styrenebutadiene copolymers andstyrene-vinylbenzylhalide copolymers; polysulfone; and polyethersulfone.Liu's MMMs contain organic or inorganic microporous molecular sieves,which inorganics may be SAPO-34, Si-DDR, AlPO-14, AlPO-34, AlPO-18, LTA,ERS-12, NaA (4A), CaA (5A), KA (3A), CDS-1, SSZ-62, UZM-9, UZM-13,UZM-17, UZM-19, MCM-65, MCM-47, medium pore molecular sieves such assilicalite-1, Si-MTW, UZM-8, SAPO-31, EU-1, ZSM-57, NU-87, Si-BEA,Si-MEL, and large pore molecular sieves such as FAU, OFF, zeolite L,NaX, NaY, and CaY. Liu reports that for a mixed matrix membrane with 30wt. % of AlPO-18 fillers in a BP-55 polymer matrix, the permeabilityincreased by 57% compared to a pure BP-55 membrane, while theselectivity increased by 17%. However, Liu does not disclose polyamides,nor multi-layered membranes, nor CDCs.

US 2009/0131242 A1 by Liu et al. (Liu 242) discloses a method of makingpolymer-functionalized molecular sieve/polymer mixed matrix membranes(MMMs) with either no macrovoids or voids of less than several Angstromsat the interface of the polymer matrix and the molecular sieves byincorporating polyethersulfone (PES) or cellulose triacetate (CTA)functionalized molecular sieves into a continuous polyimide or celluloseacetate polymer matrix. Liu 242's MMMs, esp. PES functionalizedAlPO-14/polyimide MMMs and CTA functionalized AlPO-14/CA MMMs have goodflexibility and high mechanical strength, and exhibit significantlyenhanced selectivity and/or permeability over the polymer membranes madefrom the corresponding continuous polymer matrices for carbondioxide/methane (CO₂/CH₄), hydrogen/methane (H₂/CH₄), andpropylene/propane separations. Liu 242's MMMs are reported to besuitable for a variety of liquid, gas, and vapor separations such asdeep desulphurization of gasoline and diesel fuels, ethanol/waterseparations, pervaporation dehydration of aqueous/organic mixtures,CO₂/CH₄, CO₂/N₂, H₂/CH₄, O₂/N₂, olefin/paraffin, iso/normal paraffinsseparations, and other light gas mixture separations.

Liu 242 uses a polymer matrix made from one or more polyimides (e.g.,Ultem® or Matrimid® poly(ether)imides, respectively from GE Plastics andHuntsman Advanced Materials) which have at most a single methylene groupseparating an aromatic and/or conjugated polymer backbone, but disclosesthat the polymer may be selected from a vast array of polymers with anequally vast array of inorganic or organic fillers. Liu 242 reports thatfor 50% AlPO-14/poly(3,3′, 4,4′benzophenone tetracarboxylicdianhydride-3,3′, 5,5′-tetramethyl-4,4′-methylene dianiline, i.e.,poly(DSDA-TMMDA), a mixed matrix dense film without surfacefunctionalization by PES polymer, the selectivity decreased by 47%compared to that of the “control” poly(DSDA-TMMDA) polymer. However, thefunctionalized AlPO-14/PES/poly(DSDA-TMMDA) mixed matrix showed aconsistent increase in both CO₂ permeability (by 80%) and CO₂/CH₄selectivity (65%) at loading of 0.5 (50% AIPO-14/PES/poly(DSDA-TMMDA))compared to the “control” poly(DSDA-TMMDA). Liu neither particularlyselects a polyamide membrane, nor a polysulfone membrane, nor amulti-layered membrane with each of these, nor the use of a CDC fillerin such a matrix.

U.S. Pat. No. 6,503,295 to Koros et al. (Koros 295) describes mixedmatrix membranes capable of separating carbon dioxide from mixturesincluding carbon dioxide and methane, and processes for purifyingmethane using the membranes. Koros 295's membranes are preferablypolymer membranes that include discrete carbon-based molecular sieveparticles with sizes of between about 0.5 microns to about 5.0 microns.Koros 295's particles are formed by pyrolyzing a precursor polymer inthe form of a powder or film. Koros 295's pyrolyzed polymer is thenmilled to desired small size particles, in a preferred ratio ofparticles to polymer of about 0.25 to about 1.0 by volume. A preferredmethod for preparing the mixed matrix membrane is by dispersing theparticles in a solvent, adding a small quantity of the desired polymeror “sizing agent” to “size” or “prime” the particles, adding a polymer,casting a film of the polymer solution, and evaporating the solvent toform a mixed matrix membrane film. The mixed matrix membrane filmpermits passage of carbon dioxide and methane, but at differentpermeation rates, such that the ratio of the relative permeation ratesof carbon dioxide to methane is larger through the mixed matrix membranefilm than through the original polymer. The mixed matrix membrane ispreferably in the form of a dense film or a hollow fiber. A mixturecontaining carbon dioxide and methane can be enriched in methane byselective passage of carbon dioxide over methane in a gas-phase processthrough the membrane

U.S. Pat. No. 6,585,802 to Koros et al. (Koros 802) discloses a matrixpolymer membranes capable of separating carbon dioxide from mixturesincluding carbon dioxide and methane, and processes for purifyingmethane using the membranes include a selective layer thickness ofbetween about 1000 Angstroms to about 0.005 inch, that include discretecarbon-based molecular sieve particles with sizes of between about 0.5microns to about 5.0 microns. Koros 802's particles are formed bypyrolyzing a precursor polymer in the form of a powder or film. Koros802's pyrolyzed polymer is then milled to desired small size particles.Koros 802's preferred ratio of particles to polymer is about 0.25 toabout 1.0 by volume. Koros 802's preferred method for preparing themixed matrix membrane is by dispersing the particles in a solvent,adding a small quantity of the desired polymer, or “sizing agent” to“size” or “prime” the particles, adding a polymer, casting a film of thepolymer solution, and evaporating the solvent to form a mixed matrixmembrane film, preferably in the form of a dense film or a hollow fiber.Koros 802's polymer is preferably a rigid, glassy polymer, morepreferably, with a glass transition temperature above about 150° C.

Koros 295 and Koros 802 describe that a practically unlimited selectionof polymers is useful for its matrix, limited only by diffusionproperties and preferring (esp. Ultrem® and Matrimid®) polyimides, withthese polymers being pyrolyzed along with carbon molecular sieves(CMSs), i.e., milled particles of polyimides, polyamides, cellulose andderivatives thereof, thermosetting polymers, acrylics, pitch-tarmesophase, and the like (though Koros does not limit the CMS materialsto these). Neither Koros reference discloses particularly selecting apolyamide membrane, nor a polysulfone membrane, nor a multi-layeredmembrane with each of these, nor the use of a CDC filler in such amatrix. Moreover, these references require pyrolyzing the polymericmatrix.

Accordingly, there remains a need for improved membranes and methods forseparating gases, especially CO₂ from hydrocarbon gas mixtures.

SUMMARY OF THE INVENTION

Aspects of the invention provide multilayered membrane(s), comprising: afirst layer, comprising at least 50 wt. % sulfone-containing polymer; asecond layer, comprising at least 50 wt. % polyamide comprising, incondensation polymerized form, an aliphatic diamine and an aromaticdicarboxylate; and SiC, Fe₃C, WC, Ti₃SiC₂, ZrC, B₄C, TaC, Mo₂C, and/orTiC-derived carbon (CDC) nanoparticles embedded in the second layer inan amount in a range of from 0.005 to 1.0 wt. % , based on a totalweight of the second layer, wherein the first layer directly contactsthe second layer. Such membranes may have any permutation of thefeatures described herein.

The second layer may comprise the CDC nanoparticles in a range of from0.01 to 0.9 wt. %. Additionally or alternatively, the CDC nanoparticlesin the second layer may comprise TiC-derived CDC nanoparticles.

Inventive membrane may comprise a further polyamide-comprising layercomprising the CDC nanoparticles.

The CDC nanoparticles may be prepared by a method comprising: (i)heating titanium carbide and chlorine gas at temperature in a range offrom 600 to 1000° C. for a period in a range of from 2 to 6 hours; (ii)replacing the chlorine gas with hydrogen gas at within 100° C. of theheating in (i); and (iii) replacing the hydrogen gas with inert gas andcooling.

The diamine may be a cyclic diamine. For example, the diamine maycomprise a piperazine, 4-aminopiperidine, 3-aminopyrrolidine,1,4-diaminocyclohexane, 1,4-diaminomethylene-cyclohexane,1,4-diazacycloheptane, 1,5-diazocane, hexahydropyrrolo[3,4-c]pyrrole,hexahydropyrrolo[3,4-b]pyrrole, 3,7-diaza-bicyclo[3.3.1]nonane,2,5-diazabicyclo[2.2.2]octane, 3,8-diazabicyclo[3.2.1]octane,2,5-diazabicyclo[2.2.1]heptane, ethylenediamine, 1,3-diaminopropane,1,4-butanediamine, 1,5-pentanediamine, or a mixture of two or more ofthese. The diamine may comprise at least 75 wt. %, relative to totaldiamine, unsubstituted piperazine.

The dicarboxylate may comprise a 1,3-benzenedicarboxylate(isophthalate), 1,4-benzenedicarboxylate (terephthalate),1,2-benzenedicarboxylate (phthalate), 2,6-naphthalenedicarboxylate,2,3-naphthalenedicarboxylate, 1,4-naphthalenedicarboxylate,1,5-naphthalenedicarboxylate, 1,7-naphthalenedicarboxylate,1,2,3,4-tetrahydro-1,4-naphthalenedicarboxylate,2,6-pyridinedicarboxylate (dipicolinic acid), 2,5-pyridinedicarboxylate(isocinchomeronic acid), 1H-pyrrole-2,4-dicarboxylate, or a mixture oftwo or more of any of these. The dicarboxylate may comprise at least 75wt. %, relative to total dicarboxylate, 1,3-benzenedicarboxylate with nofurther substituents.

The sulfone-containing polymer may have a structure (I), (II), (III),(IV), and/or (V), as follows: —(—Ar—SO2-)n-(I),—(—Ar′—SO2-Ar″—O-)n-(II), —(—YAr—SO₂—)n-(III),

and/or

wherein Ar, Ar′, and Ar″ are independently aromatic residues, Y and Zare independently aliphatic, cycloaliphatic, aromatic, or heterocyclicresidues, and n is in a range of from 100 to 100,000.

The sulfone-containing polymer may have a structure PSU, PES, PAS, PPSU,and/or

PSF:

The sulfone-containing polymer may preferably be PSF and/or maypreferably have a M_(w) in a range of from 10,000 to 50,000.

Aspects of the invention may provide gas filter(s) and/or gas treatmentapparatus(es), comprising any permutation of the inventive membrane(s)as described herein.

Aspects of the invention may provide method(s), comprising: passing agas mixture, comprising CO₂ and a further gas, through any permutationof the inventive membrane(s) as described herein, thereby enriching aCO₂ in an effluent gas mixture from the membrane. The further gas may bemethane.

Aspects of the invention may provide method(s) of preparing a mixedmatrix membrane, e.g., any permutation of the inventive membrane(s) asdescribed above, the method(s) comprising: (a) combining asulfone-containing polymer with a polar aprotic solvent, to obtain afirst mixture; (b) mixing an alcohol with the first mixture, to obtain asecond mixture; (c) casting the second mixture onto a surface to createa layer with a thickness in a range of from 100 to 400 μm; (d) dryingthe layer, to obtain a dried layer; (e) polymerizing, on the driedlayer, a composition comprising an aliphatic diamine, an aromaticdicarboxylate, and SiC, Fe₃C, WC, Ti₃SiC₂, ZrC, B₄C, TaC, Mo₂C, and/orTiC-derived carbon (CDC) nanoparticles, to obtain the mixed matrixmembrane comprising a CDC-doped polyamide layer upon asulfone-containing polymer layer. Inventive methods may furthercomprise: (f) repeating the polymerization so as to obtain two or morepolyamide layers on the membrane.

The polar aprotic solvent may comprise dimethyl formamide, dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, dimethyl sulfoxide,ethyl acetate, 1,4-dioxane, nitromethane, dichloromethane, chloroform,acetonitrile, and/or acetone.

The polymerizing (e) may comprise: (i) contacting the dried layer athird mixture comprising the diamine, to give an amine-treated layer;and (ii) agitating the amine-treated layer a fourth mixture comprisingthe aromatic dicarboxylate and the CDC nanoparticles.

In the inventive methods, the third mixture may comprise from 0.5 to5.0% (w/v) piperazine and water, and/or the fourth mixture may comprisesfrom 0.05 to 0.5 (w/v) isophthaloyl chloride or isophthaloyl anhydrideand hexane, and/or the CDC nanoparticles may be present in an amount offrom 0.001 to 1.0 wt. %.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 shows a flow sheet of the setup used in the permeationexperiments described herein;

FIG. 2A-D show scanning electron microscope (SEM) images of (a) a porouspolysulfone (PSF) surface, (b) a dense PSF membrane surface, (c) a purepolyamide surface, and (d) a 0.5 wt. % CDC polyamide membrane surfacewithin the scope of the invention;

FIG. 3 shows the effect of CDC nanoparticle loading on gas permeance fora mixture of CO₂ and CH₄;

FIG. 4 shows the effect of CDC nanoparticle loading on CO₂/CH₄selectivity;

FIG. 5 shows the effect of the number of polyamide layers on gaspermeance for a mixture of CO₂ and CH₄; and

FIG. 6 shows the effect of the number of polyamide layers on CO₂/CH₄selectivity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Aspects of the invention provide multilayered membrane(s), comprising: afirst layer, comprising at least 50, 75, 85, 90, 95, 97.5, 99, 99.9,99.99 wt. % or even exclusively, relative to the polymers in the firstlayer, one or more sulfone-containing polymers; a second layer,comprising at least 50, 60, 65, 75, 85, 90, 95, 97.5, 99, 99.9, 99.99wt. % or even exclusively, relative to the polymers in the second layer,one or more polyamide polymers comprising, in condensation polymerizedform, an aliphatic diamine and an aromatic dicarboxylate; and SiC, Fe₃C,WC, Ti₃SiC₂, ZrC, B₄C, TaC, Mo₂C, and/or TiC-derived carbon (CDC)nanoparticles, preferably TiC-derived nanoparticles, embedded in thesecond layer in an amount in a range of from, e.g., 0.001 to 1.0, 0.005to 0.9, 0.01 to 0.8, or 0.025 to 0.75 wt. % , based on a total weight ofthe second layer, wherein the first layer directly contacts the secondlayer.

As referred to herein, carbide-derived carbon (CDC) materials aregenerally tunable nanoporous carbons derived from carbides. A largefamily of CDC materials can be prepared from any metal carbide, such asSiC, TiC, B₄C, Ti₃SiC₂, WC, Mo₂C, Fe₃C, etc., or mixtures thereof, byselective removal of the metal atom using a halogen gas at elevatedtemperature (200 to 1200° C.). For example, the synthesis of CDC fromTiC powder can be explained by the chemical reaction shown in Equation1, below:

2 TiC(s)+3Cl₂(g)→2TiCl₃(g)+2C(s)  Eq. 1.

CDC particles generally have a surface area per unit mass, i.e.,specific surface area (SSA), in a range from 1000 to 3000 m²/g, and havea tunable pore size (0.5 to 3 nm), pore shape, surface chemistry, andSSA, e.g., by changing the synthetic conditions, composition, andstructure of the carbide precursor. Relevant SSAs could be at least 800,900, 1000, 1200, 1250, 1300, 1500, 1750, 2000, or 2500 m²/g and/or up to4500, 4000, 3500, 3250, 3000, 2750, 2500, 2250, 2000, or 1800 m²/g.

The CDC nanoparticles may preferably be TiC-derived for particularapplications, e.g., gas treatment, and/or may preferably be present inthe second layer at any of the previously discussed endpoints, and/or atleast 0.0001, 0.0005, 0.0025, 0.0033, 0.0067, 0.0125, 0.015, 0.0175,0.02, 0.03, 0.033, 0.04, 0.06, 0.075, 0.1, 0.125, 0.15, 0.175, 0.2,0.225, 0.25, 0.275, 0.3, 0.325, 0.333, 0.35 ,0.375, or 0.4 wt. %, and/orno more than 1.2, 1.1, 1.05, 0.975, 0.95, 0.925, 0.9, 0.875, 0.85,0.825, 0.8, 0.775, 0.75, 0.725, 0.7, 0.675, or 0.667 wt. % CDCnanoparticles, whereby any of these endpoints may be upper or lower endsof ranges depending upon the circumstances

For certain gas separation/enriching applications, as disclosed herein,unexpectedly superior membrane performance may be obtained with rangesof CDC nanoparticles in a polyamide layer, e.g., the second layer, in arange of from 0.01 to 0.9, 0.02 to 0.875, 0.05 to 0.85, 0.1 to 0.825, oreven 0.2 to 0.8 wt. % , based on a total weight of the second (orpolyamide-comprising) layer. Additionally or alternatively, the CDCnanoparticles in the second layer may comprise at least 75, 80, 85, 90,91, 92, 92.5, 93, 94, 95, 96, 97, 97.5, 98, 99, 99.1, 99.5, or 99.9 wt.% of TiC-derived CDC nanoparticles, relative to a total weight of theCDC nanoparticles in the layer. In the event of several polyamidelayers, the CDC nanoparticles embedded may be the same from layer tolayer, or may vary randomly, or may vary in a pattern, e.g., (a) CDC₁(e.g., TiC-derived), CDC₂ (e.g., WC-derived), CDC₁, CDC₂, CDC₁, CDC₂, .. . ; (b) CDC₁, CDC₂, CDC₃ (e.g., SiC-derived), . . . ; (c) CDC₁, CDC₂,CDC₃, CDC₁, CDC₂, CDC₃, CDC₁, CDC₂, CDC₃, . . . ; (d) CDC₁, CDC₂, CDC₁,CDC₃,CDC₁, CDC₂, . . . ; (e) CDC₁, CDC₂,CDC₁, CDC₃, CDC₁, CDC₄, . . . ;(f) CDC₁, CDC₂, CDC₃, CDC₂, CDC₃, CDC₄, CDC₃, CDC₄, CDC₅, . . . ; (g)CDC₁, CDC₂, CDC₃, . . . CDC₃, CDC₂, CDC₁, or the like.

The inventive membrane may comprise a further polyamide-comprising layercomprising the CDC nanoparticles, for example membranes may contain 1,2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20 or more polyamide-containing layers.The membranes may contain 1, 2, 3 or more sulfone-containing polymerlayers, though generally no more than the polyamide layer(s).

The CDC nanoparticles may be prepared by a method comprising: (i)heating titanium carbide, or any other carbide or combination ofcarbides used, and chlorine gas at temperature in a range of from 600 to1000° C. for a time period in a range of from 2 to 6 hours; (ii)replacing the chlorine gas with hydrogen gas at within 100° C. of theheating in (i); and (iii) replacing the hydrogen gas with inert gas andcooling. In place of, or in addition to, the Cl₂ gas, a further halogengas or gas mixture may be used, e.g., F₂, vaporized and/or liquid Br₂,and/or vaporized, solid, and/or liquid I₂. The temperature may vary,e.g., based on a gradient, or may be fixed, e.g., around 600, 650, 675,700, 725, 750, 775, 800, 825, 850, 875, or 900° C. The time period ofheat treatment may be at least 1 hour and over a range of 1, 2, 3, 4, 5,6, or 7 hours, although the heat treatment may be limited to 5, 4, 3.5,or 3 hours.

The diamine may be a cyclic diamine. For example, the diamine maycomprise a piperazine, 4-aminopiperidine, 3-aminopyrrolidine,1,4-diaminocyclohexane, 1,4-diaminomethylene-cyclohexane,1,4-diazacycloheptane, 1,5-diazocane, hexahydropyrrolo[3,4-c]pyrrole,hexahydropyrrolo[3,4-b]pyrrole, 3,7-diaza-bicyclo[3.3.1]nonane,2,5-diazabicyclo[2.2.2]octane, 3,8-diazabicyclo[3.2.1]octane,2,5-diazabicyclo[2.2.1]heptane, ethylenediamine, 1,3-diaminopropane,1,4-butanediamine, 1,5-pentanediamine, or a mixture of two or more ofthese. The diamine may comprise at least 75, 80, 85, 90, 92.5, 95, 97.5,98, 99, 99.9, or 99.99 wt. %, relative to total diamine, unsubstitutedpiperazine. The polyamide may contain, in polymerized form, no furthermonomers than the sole diamine (or diamines) and/or sole dicarbonylcompound (or dicarbonyls) than 7.5, 7, 6, 5, 4, 3, 2.5, 2, 1, or 0.5 wt.%.

The dicarboxylate may comprise a 1,3-benzenedicarboxylate(isophthalate), 1,4-benzenedicarboxylate (terephthalate),1,2-benzenedicarboxylate (phthalate), 2,6-naphthalenedicarboxylate,2,3-naphthalenedicarboxylate, 1,4-naphthalenedicarboxylate,1,5-naphthalenedicarboxylate, 1,7-naphthalenedicarboxylate,1,2,3,4-tetrahydro-1,4-naphthalenedicarboxylate,2,6-pyridinedicarboxylate (dipicolinic acid), 2,5-pyridinedicarboxylate(isocinchomeronic acid), 1H-pyrrole-2,4-dicarboxylate, or a mixture oftwo or more of any of these. The dicarboxylate may comprise at least 75,80, 85, 90, 92.5, 95, 97.5, 98, 99, 99.9, or 99.99 wt. %, relative tototal dicarboxylate, 1,3-benzenedicarboxylate with no furthersubstituents. The dicarboxylate may have no more than 25, 20, 15, 10, 5,4, 3, 2, 1, 0.5, 0.1, 0.001, or 0.0001 wt. % or no more than tracedetectable amounts of tricarboxylate compound(s), such as triacidhalides or tri-anhydrides.

The sulfone-containing polymer may have a structure (I), (II), (III),(IV), and/or (V), as follows: —(—Ar—SO₂—)_(n)—(I),—(—Ar′—SO₂—Ar″—O—)_(n)—(II), —(—YAr—SO₂—)_(n)—(III),

and/or

wherein Ar, Ar′, and Ar″ are independently substituted or unsubstitutedaromatic residues, such as phenylene, naphthylene, anthracenyl,biphenylene, or the like, Y and Z are independently aliphatic, such asmethylene, ethylene, propylene, or other C4-C8 alkyl residues, etc.,cycloaliphatic, such as 5, 6, 7, 8 and 10-membered rings, substituted orunsubstituted aromatic groups, such as phenylene, naphthylene,biphenylene, or the like, or heterocyclic residues, such as 5, 6, 7, 8and 10-membered rings, including substituents such as such as methylene,ethylene, propylene, or other C4-C8 alkyl residues, etc., and/orheteroatoms such as nitrogen, sulfur, and/or oxygen, and n is in a rangeof from 100 to 100,000, 150 to 75,000, 200 to 50,000, 250 to 40,000, 300to 30,000, 400 to 20,000, 500 to 10,000, 750 to 7,500, or 1,000 to5,000. Examples of useful sulfone-containing polymers can be found inParodi, Fabrizio, “Polysulfones,” Ch. 33 in Comprehensive PolymerScience and Supplements, Vol. 5, 1989, pp 561-591, which is incorporatedby reference herein in its entirety.

The sulfone-containing polymer may have one or more repeating units ofstructure PSU, PES, PAS, PPSU, and/or PSF:

The sulfone-containing polymer may preferably be PSF and/or maypreferably have an M_(w) in a range of from 10,000 to 50,000, 15,000 to45,000, 20,000 to 40,000, 25,000 to 35,000, or 27,500 to 32,500. Thesulfone-containing polymer may alternatively or further have an M_(n) ina range of from 10,000 to 25,000, 12,000 to 20,000, or 14,000 to 18,000,and/or the PDI may be in a range of 1.5 to 10, 1.6 to 8, 1.75 to 6, or1.9 to 4.

Aspects of the invention may provide gas filter(s) and/or gas treatmentapparatus(es), comprising any permutation of the inventive membrane(s)as described herein. Such filters or apparatuses may contain 1, 2, 3, 5,10, 20, 50, 100, 250, 500, or more such inventive membranes. The surfacearea covered by the filters may vary by application, but may be at least0.01, 0.05, 0.075, 0.1, 0.25, 0.5, 1, 2.5, 5, 7.5, 10, 15, 25, 50, 100,or 250 m², and/or no more than 1000, 500, 250, 125, 75, 40, 20, 10, 5,1, 0.1, or 0.01 m².

Aspects of the invention may provide method(s), comprising: passing agas mixture, comprising CO₂ and a further gas, through any permutationof the inventive membrane(s) as described herein, thereby enriching aCO₂ in an effluent gas mixture from the membrane. The further gas may bemethane, ethane, ethylene, ethylene oxide, acetylene, propane,propylene, isobutene, isobutene, 1-butene, 2-butene, butane, and/orbutadiene. The gas mixture may comprise 2, 3, 4, 5, 6, 7, 10 or moregases. The gas mixture may be an exhaust or syngas or PSA by-product.The gas mixture may be a refined and/or purified gas mixture.

Aspects of the invention may provide method(s) of preparing a mixedmatrix membrane, e.g., any permutation of the inventive membrane(s) asdescribed above, the method(s) comprising: (a) combining asulfone-containing polymer with a polar aprotic solvent, to obtain afirst mixture; (b) mixing an alcohol with the first mixture, to obtain asecond mixture; (c) casting the second mixture onto a surface to createa layer with a thickness in a range of from 100 to 400 μm; (d) dryingthe layer, to obtain a dried layer; (e) polymerizing, on the driedlayer, a composition comprising an aliphatic diamine, an aromaticdicarboxylate, and SiC, Fe₃C, WC, Ti₃SiC₂, ZrC, B₄C, TaC, Mo₂C, and/orTiC-derived carbon (CDC) nanoparticles, to obtain the mixed matrixmembrane comprising a CDC-doped polyamide layer upon asulfone-containing polymer layer. Inventive methods may furthercomprise: (f) repeating the polymerization so as to obtain two or morepolyamide layers on the membrane. Sulfone-containing polymer layerswithin the scope of the invention may have a thickness in a range offrom 50 to 1000, 100 to 500, 125 to 400, 150 to 300, or 175 to 250 μm,and/or the polyamide containing layer(s) may have thicknesses of no morethan 500, 400, 300, 250, 225, 200, 175, 150, 125, 100, 75, 50, or 25 μm.The polyamide containing layers may generally be thinner than thesulfone-containing polymer layer.

The polar aprotic solvent may comprise dimethyl formamide, dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, dimethyl sulfoxide,ethyl acetate, 1,4-dioxane, nitromethane, dichloromethane, chloroform,acetonitrile, and/or acetone. The polar, aprotic solvent may preferablyinclude dimethyl acetamide and THF.

The polymerization (e) may comprise: (i) contacting the dried layer witha third mixture (preferably aqueous) comprising the diamine, to give anamine-treated layer; and (ii) agitating or contacting the amine-treatedlayer with a fourth mixture (preferably in an organic solvent such ashexane) comprising the aromatic dicarboxylate and the CDC nanoparticles.

In the inventive methods, the third mixture may comprise from 0.5 to5.0, 1.0 to 4.0, 1.5 to 3.5, 1.75 to 3.0, or 2 to 2.5% (w/v) diamine,e.g., piperazine, and water or similar polar solvent, and/or the fourthmixture may comprises from 0.05 to 0.5, 0.1 to 0.4, 0.15 to 0.3, or 1.75to 0.25% (w/v) dicarbonyl compound, e.g., isophthaloyl chloride orisophthaloyl anhydride, and hexane or similar solvent(s), and/or the CDCnanoparticles may be present in an amount of from 0.001 to 1.0 wt. % (orany percentage range discussed above). Hexane, as a solvent, may besubstituted by, or supplemented with butane, pentane, cyclohexane,heptane(s), octane(s), decalin, diethyl ether, diisopropyl ether, and/oradditive-free gasoline. The diamine may be in water and/or methanol invarying proportions or any solvent to create a phase separation with thesolvent of the carbonyl compound and sufficient to dissolve the diamine.

Inventive membranes need not, but may as desired, exclude polyesterlayers and/or contain no more than 25, 20, 15, 10, 5, 4, 3, 2, 1, 0.5,0.1, 0.001, or 0.0001 wt. %, relative to total weight, or no more thantrace detectable amounts of polyesters. The second(polyamide-containing) layer generally contain less than 15, 10, 7.5, 5,2.5, 2, 1, 0.1, 0.01, 0.001, or 0.0001 wt. %, relative to polymercontent of each layer, vinylidene fluoride (VDF), tetrafluoroethylene(TFE), ethylenetetrafluoroethylene (ETFE), perfluoroalkoxyalkane (PFA),vinylfluoride (VF), chlorotrifluoroethylene (CTFE), fluorinated ethylenepropylene

(FEP), hexafluoropropylene (HFP), perfluoro (propyl vinylether),polyethylene, polypropylene, polysulfone, polyketone, polyethersulfone,cellulose, cellulose acetate, cellulose triacetate, regenerativecellulose, acryl resin, epoxy, and/or polyimide-based (co)polymers.Inventive membranes generally contain less than 15, 10, 7.5, 5, 2.5, 2,1, 0.1, 0.01, 0.001, or 0.0001 wt. % polyimide. Additionally, orseparately, the doped layers may contain no more than 25, 20, 15, 10, 5,4, 3, 2, 1, 0.5, 0.1, 0.001, or 0.0001 wt. % or no more than tracedetectable amounts of zeolites, titanium oxide, (fumed) silica, siliconcarbide, silicon nitride, spinel, silicon oxycarbide, glass powder,glass fiber, carbon fiber, graphene, nanotubes, gold microparticles,silver microparticles, alumina, magnesia, silicon nitride, zirconia,zirconium carbide, sialon, nasicon, silceram, mullite, aluminum, copper,nickel, steel, titanium, titanium carbide, and titanium diborate, SiC,WC, Fe₃C, ZrC, B4C, TaC, Mo₂C, and/or Ti₃SiC₂. Inventive polyamides maycontain no more than 25, 20, 15, 10, 5, 4, 3, 2, 1, 0.5, 0.1, 0.001, or0.0001 wt. % or no more than trace detectable amounts of tricarbonyland/or tetracarbonyl compounds. Inventive polyamides may contain no morethan 25, 20, 15, 10, 5, 4, 3, 2, 1, 0.5, 0.1, 0.001, or 0.0001 wt. % orno more than trace detectable amounts of triamine and/or tetraaminecompounds.

EXAMPLES

Carbide-derived carbon (CDC)/polyamide film(s) on top of a polysulfone(PSF) support were prepared to study the merits of such membranes forCO₂ separation from CH₄. The membranes produced, as well as CDCsnanoparticles, were characterized by SEM, FT-IR, TGA, and XRD. CO₂ andCH₄ permeation were tested for the membranes using the establishedconstant volume/variable pressure method. Gas permeation measurements ofthe membranes demonstrated 88.14% enhancement in CO₂ permeance and49.35% improved CO₂/CH₄ selectivity compared to pure polyamide on PSFmembranes. A Netzsch model STA 449 F345 Jupiter® TGA device was used tocheck the thermal stability /degradation behavior of the membranes andcomponents.

Titanium carbide nano-powder (cubic TiC, 99+%, 40-60 nm) was purchasedfrom US Research nanomaterials, Inc., USA. Polysulfone (average MW˜35,000) and dimethyl acetamide (DMAc) were purchased fromSigma-Aldrich, USA, and n-hexane was purchased from Fisher ScientificCanada.

Synthesis of CDC nanoparticles: titanium carbide (which may besubstituted by, or supplemented with, any metal carbide described hereinor otherwise known in the art) in quartz boat was inserted in a quartztubular furnace and heated at a rate of 10° C./min to the desiredtemperature while continuously purging with argon to create air-free andoxygen-free, closed system. The atmosphere may desirably contain lessthan 15, 10, 7.5, 5, 2.5, 2, 1, 0.1, 0.01, 0.001, 0.0001, or 0.00001vol. % O₂, based on the amount of all gases in the atmosphere. Theheating rate may be anywhere in a range of from 1 to 50, 2 to 40, 3 to30, 5 to 25, 7.5 to 15, or 8 to 12° C./min. When the furnace temperaturereached the desired set point of 700, 800, or 900° C., pure chlorine gaswas introduced at a flow rate of 10 to 13 cm³/min for 3 hours. Afterchlorination, a post-treatment was carried out with hydrogen gas at thesame final temperature, i.e., 700, 800, or 900° C., for one hour toremove the remaining chlorine from the CDC which will enhance the SSAand micro-pore volume of the nanoparticles. Useful temperatures may bein a range of from 200 to 1200, 400 to 1100, 500 to 1000, or 600 to 900°C., e.g., any of these endpoints or at least 300, 450, 550, 650, 675,725, 750, 775, 825, or 850° C., and/or no more than 1150, 1050, 1025,975, 950, 925, 875, 850, or 825° C. Then the furnace was purged withargon gas to cool it down to ambient temperature.

Membranes Preparation—Polysulfone Support: a polysulfone (PSF) supportwas fabricated by dry/wet phase inversion technique. Prior to membranepreparation, commercially available PSF polymer pellets were driedovernight at 100° C. in a vacuum oven in order to completely remove themoisture from the polymer. Dry PSF pellets were dissolved in a mixtureof DMAC and THF, then ethanol was added and the solution, which wasstirred for 24 hours at 25° C. using a magnetic stirrer. The polymericsolution, having a composition shown in Table 1, below, was thendegassed at room temperature for 24 hours to remove dissolved gases/airbubbles. After that, the solution was cast on a clean glass plate to athickness of 200 μm using a casting knife. The membrane was left in airfor 60 seconds under ambient condition and subsequently immersed in adeionized (DI) water bath for 24 hours. The membranes were immersed inmethanol for 2 hours for solvent-exchange and treated withpolydimethylsiloxane (3% in hexane) to eliminate infinitesimal defectsor pinholes in the membrane and then finally dried in vacuum oven at100° C. for 48 hours.

TABLE 1 Composition and amount of the dope solution Component Amount (g)Concentration (%) PSF Pellets 4.00 23.03 DMAC 5.81 33.45 THF 5.81 33.45Ethanol 1.75 10.07

Membranes Preparation—Preparation of Polyamide (PA) and CDC/PA MixedMatrix Membranes (MMMs): a polyamide membrane was prepared byinterfacial polymerization, whereby polymerization occurs between adiamine—here piperazine in deionized water—and an activated carbonylcompound (e.g., acid halide, such as acid chloride or acid bromide, oracid anhydride)—here isophthaloyl chloride in hexane. The previouslyprepared PSF layer was saturated with the 2% (w/v) piperazine solutionfor 10 minutes, then a rubber roller was used to remove the excesspiperazine solution. Subsequently, the PSF support layer was immersed inthe 0.2% (w/v) isophthaloyl chloride solution for 3 minutes, then theexcess unreacted isophthaloyl chloride was removed using pure hexane.Finally, the membranes were cured/dried at 80° C. for 10 min, and thepolyamide-polysulfone membranes were kept in DI water. For thin filmnanocomposite (TFN) membranes, CDCs nanoparticles were incorporated intothe polyamide layer during interfacial polymerization reaction by addingthe desired amount of nanoparticles, shown in Table 2, to 100 mL of theisophthaloyl chloride solution, then the CDC-doped isophthaloyl chloridesolution was sonicated for 15 minutes using probe sonicator for 1 hourin a bath sonicator.

TABLE 2 List of membrane Codes and Composition of the prepared TFNmembranes Membrane code Description MMM0 Pure polyamide membrane withoutCDC nanoparticles. (Control PA) This membrane was used as the controlsample with which, the performance of other membranes were compared MMM1Mixed matrix membrane comprises polyamide and 0.0005% CDC nanoparticlesMMM2 Mixed matrix membrane comprises polyamide and 0.002% CDCnanoparticles MMM3 Mixed matrix membrane comprises polyamide and 0.1%CDC nanoparticles MMM4 Mixed matrix membrane comprises polyamide and0.5% CDC nanoparticles MMM5 Mixed matrix membrane comprises polyamideand 1% CDC nanoparticles

After sonication, the interfacial polymerization was conducted as above.To synthesize a layer-by-layer membrane structure, the interfacialpolymerization can be repeated with multiple reactions between the samemonomers, each time after drying/curing. For each complete cycle ofinterfacial polymerization and curing/drying, the membrane can beconsidered to include one additional deposited (optionally dopedpolyamide) layer. It is also possible to vary doped and undoped layersin any pattern as discussed above.

Gas Permeation Measurements: The permeance of the fabricated membraneswas examined using pure CO₂ and CH₄ gases. The membranes were tested atdifferent feed pressures from 1 to 5 bar and temperatures from 300 to323 K. Gas permeation experiments were conducted using the well-knownconstant volume/variable pressure (time-lag) method.

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views.

As shown in FIG. 1 , the gas permeation setup was built to work in twomodes, constant volume/variable pressure and constant pressure/variablevolume. The system contains three Bronkhorst Coriolis mass flowcontrollers, a membrane module (M), a permeation volume, a vacuum pump(V) that is connected to the permeate volume (V2 to V5), and pressuretransducers (P1, P2, P3, P4) to detect the feed and permeate pressures.The process is controlled by software and the data is collected byLabVIEW. A membrane sample with an effective area of 4.91 cm² was cutand fixed inside the membrane cell, and both sides of the membranemodule were evacuated to a pressure of less than 1 mbar. The gas wasthen fed into the module at a constant pressure. To determine the gaspermeation, the valve (V4) used for the evacuation was closed and thepressure change in the permeate side was monitored with time. The leakrate was measured at the start of each experiment to get accuratepermeation rate and the data reported here is the average of at leasttwo independent measurements. The permeance (p) was calculated in gaspermeation units (1 GPU=10⁻⁶ cm³ (STP)/(s cm² cm-Hg)) using Eq. (1):

$\begin{matrix}{{p = {\frac{273.15 \times 10^{6}V_{d}}{760\left( {P_{2} \times \frac{76}{14.7}} \right)AT}\left\lbrack {\left( \frac{{dP}_{1}}{dt} \right)_{ss} - \ \left( \frac{dP_{1}}{dt} \right)_{leak}} \right\rbrack}},} & (1)\end{matrix}$

where V_(d) is the downstream volume (cm³), A is the effective membranearea (cm²), P₂ is the upstream pressure (mm Hg), and (dP₁/dt)_(ss) isthe rate of pressure change in the downstream chamber at the steadystate in (mm Hg/s), and (dP₁/dt)_(leak) is the leak rate in (mm Hg/s), Tis the cell temperature in K. The selectivity of gas i to j (α_(ij)) canbe estimated by Eq. (2):

$\begin{matrix}{\alpha_{ij} = {\frac{p_{i}}{p_{j}}.}} & (2)\end{matrix}$

SEM images of polysulfone membrane are shown in FIG. 2 . The images weremade using a MIRA3 Field Emission Scanning Electron microscope (FE-SEM)from TESCAN, with an increasing electron voltage of 15 KV. A gold layerof 10 nm thickness was used for samples coating using Ion Sputter Q 150RS (Quorum Technologies). The highly porous PSF surface, seen in FIG. 2A,was observed for membranes prepared by a conventional wet phaseinversion method. These membranes showed very low gas selectivity.Therefore, a convective air evaporation period was applied to themembranes before coagulation in a DI water bath, which resulted in anasymmetric PSF structure with a top dense layer, as can be seen in FIG.2B.

The micrograph SEM images of the polyamide surface (FIG. 2C) andCDC/polyamide MMM surface (FIG. 2D) indicate the formation of a thinlayer of composite polyamide and CDC/PA layers on top of PSF supportmembrane. SEM images show that a defect-free polyamide layer (FIG. 2C)and CDC/polyamide layer (FIG. 2D) were built on top of the PSF support,and the smooth PSF surface (FIG. 2B) was totally covered by a rough andnodular polyamide structure. The polyamide and CDC-polyamide layers wereformed as a result of interfacial polymerization reaction between thediamine (here, piperazine) and the dicarboxylate (here, isophthaloylchloride).

The gas separation performance of the multi-layer membranes, includingpolysulfone support, and (optionally CDC-doped) polyamide layer(s),fabricated according to the above procedure, was evaluated using purecarbon dioxide (CO₂) and methane (CH₄) gases at a temperature of 300.15K (27° C.) and 5 bar feed pressure are shown in Table 3, below.

TABLE 3 Gas separation performance of the fabricated polysulfonesupport, thin film polyamide membranes, and (CDCs)/polyamide MMMs at300.15 K and 5 bar. Membrane Loading % CO₂ CH₄ CO₂/CH₄ PSF 0 2.41 0.5564.33 PA 0 2.16 0.162 13.33 MMM₄ 0.5 4.07 0.204 19.92

From Table 3, overall experimental results indicate that CDC/polyamidemixed matrix membranes, e.g., MMM₄, can provide higher gas permeance andselectivity in comparison with the reference pure polyamide andpolysulfone membranes. Without wishing to be bound to any theory,enhanced gas permeation and selectivity were may be attributed to theaddition of carbide-derived carbon (CDC) nanoparticles, which can allowfaster gas flow through the membrane by disrupting the polymer chainmatrix. As indicated by SEM images in FIG. 2D, CDC nanoparticles candisperse well in the polyamide layer. Higher gas permeance may be due towell-dispersed CDC forming channels in polyamide matrix to transport gasmolecules more effectively. Furthermore, the gas selectivity of a PSFmembrane may be enhanced by including a thin polyamide layer upon thePSF layer, while the gas permeance may decrease as a result of theincreased mass transfer resistance.

FIG. 3 shows the change in CO₂ and CH₄ gas permeance by varying CDCsloading from 0.0005% to 1% in the polyamide-comprising layer for therespective membranes (MMM₁-MMM₅). The permeation rate of both CO₂ andCH₄ gas molecules may be enhanced by increasing the CDC nanoparticlescontent in the polyamide layer(s). This may be attributed to abeneficial interaction between polyamide matrix and nanofiller surface,implying good adhesion of the CDC to the polyamide chain. Moreover, highsurface areas and/or porosities of CDC may offer more surface and volumefor gases to diffuse through the membrane matrix.

As seen in FIG. 3 , even though both CO₂ and CH₄ gas permeationincreased with increasing CDC content in the polyamide layer, theincrements were not the same for the two gasses. From FIG. 3 , CO₂permeance initially increased from 2.16 GPU for pure polyamide to 2.44GPU for MMM₂ with 0.002 wt. % CDC-loading and continued to increase to3.13 GPU for 0.1 wt. % CDC-loading, while the maximum CO₂ permeance wasrecorded at 1 wt. % CDC-loading with a value of 5.00 GPU. On the otherhand, when CDC concentration was increased to 0.1 wt. %, the permeationof CH₄ increased by only 14.8%, with a maximum value of 0.375 GPUobserved at 1 wt. % CDC-loading. The unexpectedly higher increase in CO₂permeation relative to CH₄ provides improved CO₂-versus-CH₄ selectivity.

From FIG. 4 , possibly as a result of the good dispersion of CDCnanoparticles in the polyamide layer(s), the CO₂-versus-CH₄ selectivityimproved by increasing CDC loading up to a concentration of 0.5 wt. %,then the gas selectivity unexpectedly declined to 13.31 with 1.0 wt. %TiC-derived CDC-loading. The diminished selectivity of the 1.0 wt. %TiC-derived CDC-loading may arise from nanoparticle agglomeration, whichcan be observed in SEM images. CDC agglomeration indicates the creationof defects in the membrane surface, possibly resulting in higher CH₄permeance compared to CO₂. FIG. 4 shows that when CDC loading increasedfrom 0.5% to 1%, the CO₂ permeance increased by 22.8% while the CH₄permeance increased 83.82%, resulting in lower CO₂-versus-CH₄selectively.

The best-performing loading amount selected from MMM₀ to MMM₅, i.e., 0.5wt. % CDC-loaded polyamide (MMM₄), was then chosen to fabricateCDC/polyamide MMMs including multiple 0.5 wt. % CDC-loaded polyamidelayers as follows: M₁ (1 layer), M₂ (2 layers), M₃ (6 layers), and M₄(10 layers). FIG. 5 shows the permeance of CO₂ and CH₄ as a function ofthe number of 0.5 wt. % CDC-loaded polyamide layers. Both CO₂ and CH₄gas permeance were reduced as the number of the layers increased, likelydue to higher mass transfer resistance for gas permeation.

FIG. 5 shows that CO₂ permeance in 10 CDC-loaded (0.5 wt. %) polyamidelayer membrane (M₄) reduced from 4.07 GPU to 2.32 GPU. While CH₄permeation decreased from 0.204 GPU to 0.096 GPU. Reduced gas permeancewas accompanied by a moderate enhancement in CO₂-versus-CH₄ selectivity,which is shown in FIG. 6 , wherein the selectivity improved by 21% for10 selective layers. The higher selectivity for CO₂ over CH₄ withincreased layer count may be attributed to functional groups in theCDC/polyamide layer and/or to the presence of larger amount of CDC,which may enhance CDC structural properties, e.g., porosity, to allowhigher permeation of CO₂ relative to CH₄.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described herein.

1. (canceled)
 2. The method of claim 14, wherein the second layer ofeach multilayered membrane of the plurality of multilayered membranescomprises the CDC nanoparticles in a range of from 0.01 to 0.5 wt. %,and wherein the CDC nanoparticles in the second layer compriseTiC-derived CDC nanoparticles.
 3. The method of claim 14, wherein eachmultilayered membrane of the plurality of multilayered membranes furthercomprises comprising: at least one additional polyamide-comprising layercomprising the CDC nanoparticles.
 4. The method of claim 2, wherein theCDC nanoparticles are prepared by a method comprising: heating titaniumcarbide and chlorine gas at temperature in a range of from 600 to 1000°C. for a time period in a range of from 2 to 6 hours; replacing thechlorine gas with hydrogen gas at within 100° C. of the heating in (i);and replacing the hydrogen gas with inert gas and cooling.
 5. The methodof claim 14, wherein the aliphatic diamine is a cyclic diamine.
 6. Themethod of claim 14, wherein the aliphatic diamine comprises at least oneselected from the group consisting of a piperazine, 4-aminopiperidine,3-aminopyrrolidine, 1,4-diaminocyclohexane,1,4-diaminomethylene-cyclohexane, 1,4-diazacycloheptane, 1,5-diazocane,hexahydropyrrolo[3,4-c]pyrrole, hexahydropyrrolo[3,4-b]pyrrole,3,7-diaza-bicyclo[3.3.1]nonane, 2,5-diazabicyclo[2.2.2]octane,3,8-diazabicyclo[3.2.1]octane, 2,5-diazabicyclo[2.2.1]heptane,ethylenediamine, 1,3-diaminopropane, 1,4-butanediamine, and1,5-pentanediamine.
 7. The method of claim 14, wherein the aliphaticdiamine comprises piperazine and a content of the piperazine is at least75 wt. % relative to total aliphatic diamine.
 8. The method of claim 14,wherein the dicarboxylate comprises at least one selected from the groupconsisting of 1,3-benzenedicarboxylate (isophthalate),1,4-benzenedicarboxylate (terephthalate), 1,2-benzenedicarboxylate(phthalate), 2,6-naphthalenedicarboxylate, 2,3-naphthalenedicarboxylate,1,4-naphthalenedicarboxylate, 1,5-naphthalenedicarboxylate,1,7-naphthalenedicarboxylate,1,2,3,4-tetrahydro-1,4-naphthalenedicarboxylate,2,6-pyridinedicarboxylate (dipicolinic acid), 2,5-pyridinedicarboxylate(isocinchomeronic acid), and 1H-pyrrole-2,4-dicarboxylate.
 9. The methodof claim 14, wherein the dicarboxylate comprises1,3-benzenedicarboxylate and a content of the 1,3-benzenedicarboxylateis at least 75 wt. %, relative to total dicarboxylate.
 10. The method ofclaim 14, wherein the sulfone-containing polymer of each multilayeredmembrane of the plurality of multilayered membranes is of formulae (I),(II), (III), (IV) or (V):

wherein Ar, Ar′, and Ar″ are independently aromatic residues, Y and Zare independently aliphatic, cycloaliphatic, aromatic, or heterocyclicresidues, and n is in a range of from 100 to 100,000.
 11. The method ofclaim 10, wherein the sulfone-containing polymer comprises at least oneselected from the group consisting of


12. The method of claim 11, wherein the sulfone-containing polymer isPSF having a M_(w) from 10,000 to 50,000.
 13. (canceled)
 14. A method,comprising: passing a gas mixture, comprising CO₂ and at least oneadditional gas, through a gas filter to form a permeate that is enrichedin CO₂ content and a gaseous composition having a concentration of CO2that is less than a concentration of CO2 in the gas mixture, wherein thegas filter comprises: a plurality of multilayered membranes fixed insidea cell; wherein each multilayered membrane of the plurality ofmultilayered membranes comprises: a first layer, comprising at least 50wt. % of one or more sulfone-containing polymers; a second layer,comprising at least 50 wt. % of one or more polyamides comprising, incondensation polymerized form, an aliphatic diamine and an aromaticdicarboxylate; and at least one carbide-derived carbon (CDC)nanoparticles selected from the group consisting of SiC, Fe₃C, WC,Ti₃SiC₂, ZrC, B₄C, TaC, Mo₂C, and TiC-derived nanoparticles, wherein theCDC nanoparticles are embedded in the second layer in an amount of from0.005 to 0.5 wt. %, based on a total weight of the second layer, whereinthe first layer directly contacts the second layer.
 15. The method ofclaim 14, wherein the at least one additional gas is methane. 16-20.(canceled)